1. Field of the Invention
The present invention relates generally to a gas turbine engine, and more specifically for an air cooled turbine blade.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
A gas turbine engine includes a turbine with one or more stages of stator vanes and rotor blades that react with a hot gas flow to produce mechanical work. The turbine, and therefore the engine, efficiency can be increased by passing a higher temperature gas flow into the turbine. However, the highest turbine inlet temperature is limited to the material properties of the turbine, especially for the first stage airfoils (vanes and blades) since these are exposed to the highest temperatures in the turbine.
One way to allow for higher turbine inlet temperatures is to provide for improved cooling of the airfoils. A large amount of cooling air could be used, but the work used to compressor the cooling air is done by the engine itself in the compressor. Thus, turbine airfoil designers try to maximize the cooling capability of the airfoils while using a minimal amount of cooling air. FIG. 1 shows a prior art blade with a near wall cooling design formed in the airfoil main body with radial cooling air channels plus resupply holes in conjunction with film discharge cooling holes. cooling air from a cooling air supply cavity formed within the airfoil main body is metered through metering holes to produce impingement cooling in the radial extending cooling channels to cool the backside surface of the pressure side and suction side walls, and then discharges the spent impingement cooling air through rows of film cooling holes to provide a layer of film cooling air onto the external surface of the airfoil. A row of trailing edge exit holes connects to the cooling supply cavity to provide convection cooling for the trailing edge region. In the prior art FIG. 1 airfoil cooling design, the spanwise and chordwise cooling flow control due to airfoil external hot gas temperature and pressure variations is difficult to achieve. In addition, a single pass radial channel flow is not the best method of utilizing cooling air and results in a low convection cooling effectiveness.